A problem long-standing in the art lies in the production of pneumatic tires and wheels which, when assembled and operated on a vehicle, run true about their axis of rotation. Forces generated by any circumferential variations in the tire carcass and/or out-of-round condition in the tire or wheel cause vibraions, which in turn lead to dissatisfied customers and significant warranty claims against automobile manufacturers. The present trend among manufacturers toward higher tire inflation pressures and smaller vehicles to improve fuel economy accentuates this problem, so that uniformity of radial runout and force vibrations of the tire and wheel assembly has become more critical than in the past.
Vehicle wheels conventionally include a circular array of disc bolt openings adapted to receive mounting studs for mounting the wheel to a vehicle, and a center-pilot opening adapted to be received over the wheel hub. It has been and remains conventional practice in the industry to attempt to form the bolt mounting circle and center-pilot openings co-axially with each other and with the tire rim bead seat, with the goal thus being a perfect true-running wheel. A number of techniques have been proposed for accomplishing this result, including formation of the bolt and center openings with a single tool while locating off of the bead seat, machining the center opening while locating off of the pre-formed bolt-mounting openings, and/or circumferentially permanently deforming the rim bead seats while locating off of the bolt-mounting and/or center-pilot openings.
Gregg U.S. Pat. No. 3,688,373 discloses apparatus for rounding and forming vehicle wheels. A disc and rim assembly having preformed bolt and center openings is fixtured in a die by pins received into the bolt openings. With the bolt-hole circle so located, rim-rounding dies are reciprocated against the rim bead seats, which are initially oversize, to plastically deform the bead seats with respect to the fixtured bolt-hole circle. With the wheel so deformed and clamped, additional sizing may be performed on the bolt holes by supplemental punches, and the center opening may be deformed by bringing the clamped rim and disc against a center-hole forming tool.
The machine and process disclosed in the Gregg patent suffer from a number of deficiencies in both theory and practice. First of all, it is not possible to locate the bead seat axis, and/or to control radial runout from the average bead seat axis, employing a rim-deformation process of the character disclosed to accuracy currently specified by industry standards. Secondly, elasticity in the rim and disc preclude accurate location of either the bolt or center opening axis with respect to the average bead seat axis, let alone accurate location of both opening axes with respect to the average bead seat axis and with respect to each other. Thirdly, it is extremely difficult in the forming apparatus disclosed in Gregg to vary the location of the bead seat, bolt-hole and center-opening axes with respect to each other.
A particular problem is encountered in connection with so-called styled wheels which possess a deep-drawn neck or cone integrally projecting from the disc surrounding the center-pilot opening to simulate a styled hub cap. It is conventional practice in manufacture of such wheels to machine the inside surface or ID at the base of the styled neck or cone while locating off of the bead seats to obtain concentricity between the center opening and bead seats. Such a separate machining operation is expensive to implement and tends to weaken the disc structure at the base of the styled center cone.
Daudi et al U.S. Pat. Nos. 4,279,287 and 4,354,407, both assigned to the assignee hereof, depart from the conventional practice of attempting to form a true-running wheel, and address the problem of radial runout and/or radial force variations in a pneumatic tire and wheel assembly by intentionally forming the bolt-mounting and/or center-pilot openings in the wheel disc at the time of wheel manufacture on an axis which is eccentrically offset from the average axis of the bead seats on the wheel rim. This offset is in a direction and amount which is predetermined to locate the low point or high point of the first harmonic of beat seat radial runout circumferentially adjacent to a selected location on the wheel rim. In the preferred embodiments, the low point of the first harmonic of bead seat radial runout lies substantially within a quadrant centered about the valve hole in the rim. A pre-tested tire having the location of the high point of the first harmonic of radial force variation marked thereon may then be assembled onto the wheel such that the respective tire and wheel harmonics are complementary and thereby tend to cancel each other.
In the preferred wheel forming apparatus disclosed in the above-noted Daudi et al U.S. patents, the bolt and center-pilot openings are formed by separate punches fixedly mounted on a single punch assembly which simultaneously punch-forms all of the openings in a wheel disc while the wheel is located by fixturing the same about the rim bead seats. Although the method and apparatus disclosed in the reference patents, as well as the wheels formed thereby, have enjoyed substantial success and acceptance in the art, a problem lies in the fact that the relationship of the bolt hole circle and center-pilot opening with respect to each other is fixed at the time of die manufacture and cannot be readily adjusted thereafter. Another problem is encountered in connection with application of this technology to manufacture of styled wheels wherein the center-pilot surface at the base of the styled disc cone cannot be readily formed while the bolt hole openings are formed.